The long-range objective of this project is to understand the functions and the activities of the plasminogen-plasmin-streptokinase system in terms of the structures and the structural changes of these proteins. The research goals of this work are: (a) to further define and quantify the functional changes of the plasminogen activator complex and of each of its dissociated components, (b) to define the chemical structure and the structural changes, their location and order of appearance through quantitative N-terminal amino acid sequence determination of streptokinase, modified streptokinase, plasminogen and plasmin at various times during their interaction, (c) to define conditions for developing crystals of activator complex of sufficient stability and quality to permit X-ray crystallographic examination.